Hydrothermal liquefaction of algae: A possible green alternative to petroleum-based bitumen-A review on wholly bio-based binders

This literature review examines 100% bio-based binders (bio-binder) derived from algal biomass as a sustainable alternative to petroleum-based bitumen in the pavement construction industry. The traditional use of bitumen contributes significantly to greenhouse gas (GHG) emissions and environmental deterioration, highlighting the critical need for renewable, low-carbon emitting materials in response to global initiatives. Algal biomass, particularly through hydrothermal liquefaction (HTL), offers a promising alternative due to its quick growth, high lipid content, and capacity to survive in various settings, including non-arable lands and wastewater. HTL effectively transforms wet algal biomass into high-quality bio-crude oil, which may then be processed into bio-binders. Studies show that these bio-binders can match or outperform standard bitumen in terms of durability and mechanical performance. The economic feasibility of bio-binders is increasing as crude oil prices rise and biotechnology advances. Additionally, algae cultivation sequesters CO 2 , which may offset emissions from bio-binder manufacturing. The transition to bio-binders has major environmental and economic benefits, such as lower carbon footprints and new market potential in renewable energy. However, issues including scalability, production costs, and energy usage arise. This paper provides a complete overview of current research, technological achievements, and future possibilities, emphasizing bio-binders' potential to alter road construction sustainably. Collaboration between governments, industry, and researchers is required to develop supportive policies and technology for widespread adoption. • Algal bio-binders via HTL offer sustainable solutions for pavement applications. • HTL efficiently converts wet algae to high-quality bio-crude versus pyrolysis. • Algal bio-binders closely replicate petroleum bitumen’s rheological properties. • Future research must target testing, LCA, characterization, and standardization.